Air brake systems for a vehicle such as a bus, truck, trailer and other heavy-duty vehicles or the like typically include a brake shoe and drum assembly which is actuated by means of an actuator assembly operated by the selective application of compressed air. Conventional air brake actuators have both a service brake actuator for actuating the brakes under normal driving conditions by the application of compressed air and also a spring-type emergency brake actuator which causes actuation of the brakes when air pressure has been released. The emergency brake actuator includes a strong compression spring which forces application of the brake when air is released. This is often referred to as the spring brake.
When applying the parking brakes, the spring brake actuator pressure is discharged from the pressure chamber and the large force compression spring pushes the spring piston and the diaphragm toward the dividing wall between the spring brake actuator and the service brake actuator. In this position, the actuator rod connected to the spring piston is pushed forward extending into the service section through the dividing center wall applying the parking or emergency brakes and thus forcing the vehicle to stop or remain parked. To release the parking brake, the pressure chamber is closed to the atmosphere and pressurized air is introduced into the pressure chamber of the spring brake actuator which expands the pressure chamber, moving the diaphragm and spring piston toward the opposing end of the spring brake actuator housing, thereby compressing the strong compression spring.
U.S. Pat. No. 6,006,651 (Pierce et al.) teaches a spring brake having an actuator with an opening provided with a bearing having at least one annular recess which accommodates at least one O-ring seal. U.S. Pat. No. 5,377,579 (Pierce) teaches a spring brake having an actuator with one or more O-ring seals through which the spring brake actuator rod reciprocates.
U.S. Pat. No. 3,977,308 (Swander, Jr. et al.) teaches a brake actuator having an opening where a retainer ring is positioned which retains a nylon and small seal or O-ring positioned in said opening. U.S. Pat. No. 3,813,994 (Swander, Jr. et al.) teaches a spring brake actuator having a seal and guide bushing retained by a ring. United States Patent Application No. 2008/0083325 A1 (Scheckelhoff et al.) teaches a spring brake actuator having bearings and seals for fluid reciprocation of the connecting shaft within the aperture. United States Patent Application No. 2007/0034465 A1 (Thompson et al.) teaches a flexible bushing assembly for a spring brake push rod seal having a sealing member to engage the push rod. Thompson et al. also teach a threaded section. United States Patent Application No. 2007/0131498 A1 Li et al. teaches a sealing member of one or more O-ring seals positioned around a push rod.
However, none of the above mentioned patents teaches a spring brake center seal design which involves dynamic sealing elements that seal in a smooth hole, bore or cavity, where the sealing element or element stack is retained in the hole, bore or cavity on each end by a bearing for the center pushrod or center tube.
Furthermore, none of the above mentioned patents teach a spring brake center seal design which has a sealing element separator between two sealing elements, such that less complicated machining is required to achieve a proper surface finish for sealing with the smooth hole or bore or cavity design since it is a through hole rather than in a groove.
As none of the prior art teaches such a design, it is desirable to provide such a sealing assembly and method for making such a sealing assembly.
It is further desirable to provide a spring brake center seal design which involves dynamic sealing elements that seal in a smooth hole or bore, where the sealing element or element stack is retained in the hole or bore on each end by a bearing for the center pushrod or center tube.
It is further desirable to provide a spring brake center seal design which has a sealing element separator between two sealing elements, such that less complicated machining is required to achieve a proper surface finish for sealing with the smooth hole or bore design since it is a through hole rather than in a groove.